CharAT ergonomics 129

CharAT machinetutorial

130 CharAT ergonomics

CharAT ergonomics 131

CharAT machinetutorial

In this tutorial we are going to explain step by step how to use CharAT Machine on a specific exam-ple.

1. Initial geometry

For the beginning we need a 3ds Max file of the object. This should include the basic geometry of the object. It is practical if we ask the engineer or designer to export the drawing so that the ma-chine is structured, each part of it is a separated element. Otherwise we should divide the object into different elements.

2. Understanding how the machine works

In order to be able to build a proper CharAT Ma-chine object we must have a full understanding of the features and size of the machine. Without it, serious problems may occur later during the workflow. The best and most practical solution is if we ask the engineer or designer to provide the full technical specifications and drawings indicat-ing the dimensions of the machine. We must have a full understanding of the degrees of freedom for each element of the machine.

Frame Adjustments description (CRUZBIKE CUERVO)In all cruzbike front wheel drive designs the crank rotates around the front wheel to provide leg ad-

1. The initial geometry imported from solid Works

2. The dataset part list

3. The technical part list

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justment. The amount of adjustment is set by a telescoping tube (US Patent 7753388) connecting bottom bracket to handlebar. The ability to pack into an OS1 sized box for eco-nomic shipping from warehouse to end customer is very important.In this design, the handlebar is welded directly to the slider. There is no clamp and no stem. When the telescoping tube adjusts, the handle bar angle also changes.Adjustments to the bicycle are performed by the following (in order of convenience):

• The handlebar is connected to the crank by a slider (red) which houses a telescoping boom (silver). This telescoping tube is the principle means of fitting riders of varying leg lengths.

• The red slider can be positioned within the slider clamp that connects it to the top of the fork steering tube, thereby changing the reach distance for the arms.

4. The adjustment DOF definition

5. The 3d dataset position, orientation and name convention

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• The seat back can be adjusted for tilt by a seat post (not shown) from low (almost touching the rear tire) to high. An angle of 47 degrees from the horizontal is typical.

• A curved downtube supports the seat pan, which can be re-positioned further up or down the curve.

• The slider clamp can be adjusted verti-cally up or down the fork steering tube.

3. Creating the bone structure

In CharAT Machine we represent the structure of the machine with bones, each element of the structure is substituted with a bone. The whole ki-nematic chain is built with the help of the bones and the bone structure. Creating a bone goes exactly the same way as in CharAT Human, you can find its description in the CharAT Human User Manual.

Before you start creating the bone structure you must note an important step. Every bone has to be identified not only by index, but by name too. Each bone is given an index numer by the pro-gram, but it is highly recommended that you also give it a name that later helps you identifying it. In case of complicated machines this action may be a great help during the workflow. In the Control dialog box, click on Bone Structure tab. Here you can set all the important parameters of the bone (as explained in CharAT Human User Manual).

6. Build the cinematic structure

7. adjust the geometry parts to the cinematic structure

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9. attach the first geometry to the cinematic struc-ture with the get mesh function

Another key factor of building a proper kinematic chain is the correct bone hierarchy. Note that set-ting the proper root of a new bone is an essential step and has to be done carefully. You can change the root of a new bone by typing the index of the root bone into the Parent text box in Control dialog box’s Bone Structure tab.

You can create a new bone by clicking on New Bone button in Control dialog box’s Bone Struc-ture tab. You can change the parameters of each bone the same way as described in CharAT Hu-man User Manual. First we suggest you to set the parameters by clicking on Modify tab in the upper-middle left side of the window. Then select the bone, click on Control button in the Menu, then go to Bone Structure tab in the pop-up dialog box. If you are ready with these parameters, click on Bone Animation tab in the same dialog box. Here first you are advised to set the degrees of freedom of the bone. This can be set with the help of the checkboxes in the upper middle part of the dialog box. There are three columns and three rows indi-cating the degree of freedom (rotation, translation and factorization) and their axes (X, Y and Z). You can enable and disable them with the checkbox-es. Under the checkboxes you can set the limit values of the enabled degrees of freedom.

In the Assignment section you can set how a par-ticular object shall move depending on how other objects of the machine move. You can select the sourse object by clicking on it after choosing Se-lect button or by typing its index number in the textbox. You can set the rotation values in differ-ent axes (Rx, Ry, Rz), the translation (Tx, Ty, Tz) and factorization (Fx, Fy, Fz) values in different axes.

If you select Inverse radio button in Target Anima-tion section at the upper left corner of the dialog box, a marker box will appear around the selected bone object. With this option you enable inverse kinematics. You can also check Reverse option for reverse kinematic movement.

As an additional option you can define control elements for each bone. With their help you can add additional movement options for the selected

8. define and modify the cinematic chain proper-ies

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10. attach the next geometry to the cinematic structure with the get mesh function

bone while the markers stay in one place and in-verse kinematics continues to work as well. For creating a control element, you need to create a new bone and in Control window’s Bone Struc-ture tab you need to check the Director checkbox. Then you have to click on Bone Animation tab and define the connection in the Assignment section as described above.

4. Merging the bone structure with the initial geometry data

After you are ready with the bone structure, you can merge it with the initial 3ds Max file. You can do it by clicking on Import in File menu then choosing Merge. As a result you can see your bone structure together with the original file.

Now it is practical to hide the original file’s objects and only view your bone structure. You can hide objects by clicking on Display tab in the upper-middle right side of the window, and you click on Hide by Name button in Hide menu. Then we suggest you to systematically unhide the original drawing objects starting from the root of the kine-matic chain.

The next step is to select the root or parent bone that you would like to attach the element(s) of the original drawing object to. After you selected the bone, click on Modify tab in the upper-middle right side of the window and go to Graphics menu. You can select the bone by typing its index into the textbox or by clicking on it, but if you have Con-trol dialog box open, you can select it even by its name.

First it is practical to choose material for the ob-ject. In Graphics Menu choose the object in Face-Material section, then click on Material Editor but-ton. In the Material Editor, you can choose the material at the same way as in CharAT Human (you can find its description in CharAT Human User Manual). You can choose from the default materials of the program or open and load your own material library.

After that you have to click on Get Mesh button. Now the program substitutes the original object by

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11. test the cinematic model

12. define the SIP for the human model position

a new one that has been created by the program, so the original object can simply be deleted. We suggest you to do this step for every object that has the same root bone, this way you can avoid confusion. Apply this step to all the objects and elements until you finish with the whole model.

5. Connecting your machine with a CharAT Hu-man object

After you finished working on your machine ob-ject, you will need to link it to a CharAT Human object. First you have to create a human model based on the description given in CharAT Human User Manual.

Note that inverse kinematics has to be enabled for the following steps. The process can be done with the Select and Link option of the 3ds Max. You have to select the marker of the human model that you wish to link to a particular marker of the machine. Then you have to click on Select and Link button in the upper left part of the 3ds Max menu. You can choose the marker of the machine from a list by clicking on Select by Name button in the 3ds Max menu or by choosing the marker with your mouse.

6. Saving and opening of the model, importing objects

You can save your finished work in different file formats that we are going to describe in this para-graph.

Machine: simply saves the whole model in a CharAT Machine file.Motion: saves the model in the animated state. Please note that if you re-open the CharAT Ma-chine file and change the name of an object, the animation can not be applied to that particular ob-ject again, but it will work for the unchanged ob-jects. Structure: saves the kinematic chain indepen-dently from the graphics. Graphics: saves the graphics independently from the kinematic chain.

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13. adjustable seat model

Please also note that the particular objects and elements of the machine can be saved indepen-dently as .cat-graph files. With the help of this op-tion you can use particular parts of the machine for a different project later.

If you would like to open a CharAT Machine file, at first you need to create a random bone that can be deleted after loading the file. Then go to File I/O Menu, click on Load and choose your file.

For importing a particular object you need to click on Import button in File I/O menu and choose the file you wish to import.

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14. using the CharAT mechanics components in complex analysis scenarios

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